The present invention relates generally to surge protectors for use with, for example, telecommunication lines. More particularly, the invention relates to a surge protector with interacting varistors for use in a telephone central office.
Wired telecommunications rely on telephone lines to facilitate voice and data transmissions. Because of the proliferation of uses for telephone lines, there has been a growing concern to protect operating personnel and/or connected communications equipment from excessive voltages and currents. Excessive voltages and currents may be caused by, for example, lightning strikes, power line crosses, and/or currents induced from adjacent power lines.
Primary telecommunications protectors, at a minimum, provide overvoltage protection. This is typically done with at least one protection element that is inserted between a conductive tip element of a surge protector and ground. Likewise, typically at least one protection element is inserted between a conductive ring element of the surge protector and ground. When a hazardous overvoltage is present on a line, the overvoltage protection element changes from a high impedance to a low impedance state, effectively shorting the hazardous overvoltage and its associated overcurrent to ground and away from equipment and/or personnel.
There are occasions when an excessive current may be present with no overvoltage. This is typically called a xe2x80x9csneak currentxe2x80x9d and may occur when there is AC induction on the line or when the tip and ring conductors are somehow shorted, or nearly shorted, to ground. During such a condition, the overvoltage protection element may not short to ground, thereby allowing hazardous overcurrents to pass by the protector to the equipment and/or personnel. Over time, the sneak current condition may cause excessive damage to the telecommunications equipment.
The present invention is directed to a central office surge protector including a tip element, a ring element, a ground element, and at least one pin. The at least one pin is electrically connected to one of the tip element, the ring element and the ground element. The central office surge protector also includes at least one gas tube having an electrode in electrical contact with at least one of the tip and ring elements, the at least one gas tube having a DC breakdown voltage and an impulse breakdown voltage that is higher than the DC breakdown voltage, and at least one varistor, wherein the at least one varistor and the at least one gas tube are electrically connected in parallel to the ground element. The at least one varistor having a clamping voltage at 1 mA being set such that the varistor will lower the impulse breakdown voltage of the at least one gas tube, yet not burn out in response to surge voltages within a predetermined range of DC breakdown voltages.
The present invention is also directed to a central office surge protector including a tip element, a ring element, a ground element, and at least one pin. The at least one pin is electrically connected to one of the tip element, the ring element and the ground element. The central office surge protector also includes at least one gas tube having at least one electrode in electrical contact with at least one of the tip and ring elements, the at least one gas tube having a DC breakdown voltage and an impulse breakdown voltage that is higher than the DC breakdown voltage, at least one sneak current protection element, and at least one varistor, wherein the at least one gas tube and the at least one varistor are electrically connected in parallel to the ground element. The at least one varistor having a clamping voltage at 1 mA being set such that the varistor will lower the impulse breakdown voltage of the at least one gas tube, yet not burn out in response to surge voltages within a predetermined range of DC breakdown voltages.
The present invention is still further directed to a central office surge protector including a tip element, a ring element, a ground element, and at least one pin. The at least one pin is electrically connected to one of the tip element, the ring element and the ground element. The central office surge protector also includes at least one gas tube having an impulse breakdown voltage and a DC breakdown voltage and at least one varistor. The DC breakdown voltage of the gas tube being in a range between a predetermined minimum and maximum value, and the impulse breakdown voltage being higher than the predetermined maximum DC breakdown voltage. The at least one varistor and at least one gas tube are electrically connected in parallel to the ground element. The at least one varistor having a clamping voltage at 1 mA between the predetermined minimum and maximum DC breakdown voltages of the at least one gas tube such that the varistor clamps the voltage during a voltage surge to reduce the impulse breakdown voltage of the gas tube without the varistor burning out.